IMIS - Marine Onderzoeksgroepen

Twenty-nine plankton tows were collected at different water depths in the equatorial and northern Pacific Ocean during the Hudson 70 cruise. Thirty planktonic foraminiferal species, belonging to eleven genera and three families, have been identified. Absolute and relative abundance of individual species, their size, structural modifications, and coiling directions of the tests are compared with the physical and chemical parameters of the Pacific Water masses. Five major groups of species including warm tropical, warm temperate, cold temperate, cold water and cosmopolitan, were mapped in three different water masses designated here as- Southern, Central and Northern or subartic. The abundance ratio of specimens in surface compared to sub-surface waters is approximately 5:1. A weak direct relationship exists between water temperature and salinity and the absolute abundance of species diversity of the foraminifera population. There appears to be no simple relationship between size, maturity of forms and various physical factors generally considered to affect the entire faunal assemblage. Kummerform development appears to be an ontogenic feature more or less independent of surrounding physical conditions. Typical specimens of Globigerina pachyderma (Ehrenberg) occur in large number in the Northern water mass of the Pacific. Reproduction cycles of several species (e.g. Globorotalia scitula (Brady) and Globorotalia truncatulinoides (D’Orbigny)) are confirmed indirectly, based on the extreme paucity of specimens in the samples analyzed for this study. Plankton tows were collected with a modified Benthos Multiple Plankton Sampler fitted with 200-micron mesh nets. The device was initially submerged to a depth of 25 metres and towed at a speed of about 1.5 knots for 15 minutes. Two additional tows were made during each cast at 350 and 750 metre depths respectively. The samples collected represent planktonic specimens resident in the 0-200, 200-500, and 500-1000 metre water layers respectively. It is assumed, however, that the concentration of planktonic formanifera is roughly constant in the water layers and that there is no appreciable diurnal change in the faunal population. The volume of water filtered through the nets was monitored using the TSK flow water meter attached to one side of the sampler frame. It was integrated with a Benthos Model 1023 acoustic telemeter. The samples were washed from each net and preserved in 10% formalin solution buffered with hexamethylene tetramine. In the laboratory, the plankton samples were split into a number of fractions depending upon their plankton concentrations. This procedure was used to reduce the final subsample to a convenient size. On the average, the half-splitting was found to be satisfactory. The split sample was sieved through a 63-micron mesh and the strained material then ignited in a low temperature TRACELAB LTA 600 asher to remove the organic constituents (Vilks, 1970). After ashing the samples were washed with water and later transferred to a disposable Millipore petri dish. The foraminiferal counts and other morphological observations were made on this petri dish using binocular microscopy. Detailed morphological features were studied using a JEOL Scanning Electron Microscope. OBIS Schema concepts implemented in this data set are: Res_Name, DateLastModified, InstitutionCode, CollectionCode, BasisOfRecord, Kingdom, Genus, Species, Collector, YearCollected, MonthCollected, DayCollected, TimeOfDay, Longitude, Latitude, MinimumDepth, MaximumDepth, FieldNumber, CatalogNumber, SampleSize, ScientificName, ScientificNameAuthor, LifeStage, Sex, ObservedIndividualCount, Phylum, Class, Order, Family, Subgenus, Subspecies, ObservedWeight, Notes (AphiaID: value).